1. Field of the Invention
This invention relates to position sensors.
2. Description of the Related Art
A linear variable differential transformer (LVDT) is a device which is used for sensing the position of objects in industrial machinery. For example, in machines which produce steel pressings (such as car body panels), there is a requirement to check the dimensions of the pressings after production (a process called gauging). This is done using an array of LVDTs, mounted in a frame, to measure the panel's dimensions and shape. A typical LVDT, see FIG. 1 of the accompanying drawings, consists of a rod 10 (the moving part) and a cylinder 12 (the fixed part).
The end of the rod may have a nut fastening 14 as shown or a contact probe. The cylinder 12 contains a primary transformer winding 16 (see FIG. 2) and two secondary transformer windings 18, 20 which are used to detect the position of a core 22 mounted on the end of the rod 10.
LVDTs have an accuracy of as little as one micron (a thousandth of a millimetre) and can be constructed as large as is necessary. LVDTs which can accommodate displacements of a meter are not uncommon.
Applicant is aware of many patents which disclose position sensors of the LVDT type discussed above. Applicant is also aware of a non-LVDT type of position sensor which has recently been disclosed in U.S. Pat No 6,489,899B1.
The present invention seeks to provide a sensor which is an improvement of the LVDT and non-LVDT types of position sensor discussed above.